Method of storing hydrogen



United States Patent Int. '01. F17c 11/00 s. on. 624-48 l 3 ClaimsABSTRACT OF THE DISCLOSURE A method for storing hydrogen whereby gaseoushydrogen is adsorbed by titanium-iron alloys at temperatures. above C.and pressures above 14 pounds per square inch.

PRIOR ART Hydrogen is conventionally stored in pressure vessels whichare dangerous both from fire and explosion hazards. Others in the arthave tried to form stable metal hydrides in order to eliminate thehazards arising from containment of hydrogen in pressurized containers.The metals and alloys previously employed by those skilled in the arthave been too expensive toallow their widespread use in conventionalprocesses such'as rockets and fuel cells.

In US. Patent No. 3,315,479, R. H. Wiswall, Jr., and J. I. Reilly,issued Apr. 25, 1967, disclosed a method of storing hydrogen wherebygaseous hydrogen is adsorbed by nickel-magnesium alloys at temperaturesabove 250 C. and pressures above 18 pounds per square inch. The hydrogenloaded alloys disclosed in U.S. Patent 3,315,479, when heated totemperatures of 250 C. give oif hydrogen at a pressure of slightly overone atmosphere. I

US. Patent No. 3,375,676, James J. Reilly and Richard H. Wiswall, Jr.,issued Apr. 2, 1968, entitled Method of Storing Hydrogen, disclosed amethod of storing hydrogen whereby gaseous hydrogen is adsorbed bycoppermagnesium alloys at temperatures above 250 C. and pressures above30 pounds per square inch. The hydrogen loaded alloys disclosed in US.patent application S.N. 642,289 when heated to temperatures of 200 C.give off hydrogen at a constant pressure. v

It is an object of this invention to provide those skilled in the artwith a simple, economical, safe method of storing hydrogen.

SUMMARY OF THE INVENTION The invention described herein was made in thecourse of, or under a contract with the US. Atomic Energy Commission.

A novel method for storing hydrogen by forming a hydrogen metal alloycomplex, wherein hydrogen gas is absorbed into a metal alloy, comprisingcontacting gaseous hydrogen with a solid titanium-iron alloy, said alloycontaining from about 35 weight percent to about 75 weight percenttitanium based upon the total weight of the titanium-iron alloy and fromabout 25 weight to about 65 weight percent iron based upon the totalweight of the titanium-iron alloy, while maintaining said hydrogen andsaid alloy at a pressure of at least about 14 pounds per square inch andat a temperature of at least about 10 C. until said alloy has absorbedup to about 3 weight percent hydrogen based upon the total weight of thetitanium-iron alloy.

DESCRIPTION OF THE INVENTION The amount of hydrogen that can be absorbedby our amount of titanium contained in the alloy. The rate of adsorptionof the hydrogen onto our novel complex is rapidwhen low temperatures(about 25- C.) and pressures of about 400 p.s.i. are employed in theloading operation. When higher temperatures are employed during theloading operation, of course higher pressures will be required. v

The product formed by our method is a hydrogentitanium-iron complex,whose exact physical and chemical structure is not known at this time.

,The hydrogen-titanium-iron complexes produced by the practice of ourinvention are capable of emitting hydrogen at a pressure of about 3atmospheres at ambient temperatures (20 0-). They can be readily storedby forming the complex inaccordance with the method disclosed by ourinvention and maintaining the complex in a pressure vessel. A more rapidrelease of the hydrogen can be effectuated by applying heat to thecomplex. To release the hydrogen from the complex, all that is requiredto be done is to allow the hydrogen to escapefrom the vessel in which itis contained.

A unique feature of our novel complexes is the fact that hydrogen isreleased at a constant rate from a complex when the complex ismaintained at a specific temperature of 25 C. until the complex containsless than 1.0 weight percent of hydrogen based on the total weight oftitaniumiron alloy contained in the complex. For example, a hydrogentitanium-iron complex containing 2 weight percent hydrogen based uponthe weight of the titanium-iron alloy upon being heated at a constanttemperature of 25 C. will maintain a hydrogen pressure of 15 lbs. persquare inch above the alloy until above 1.0 weight percent of hydrogenremains in the complex. This feature provides those skilled in the artwith a simple hydrogen source in which the rate of release can becarefully controlled by simply controlling the temperature of thecomplex during the release. Thus, it will be apparent to those skilledin the art that our invention can be readily adapted to conventionaltechniques to provide a safe dependable source of hydrogen for amultitude of uses such as rockets, fuel cells, etc.

Further, as will be readily apparent to those skilled in the art, thenovel hydrogen-titanium-iron complexes disclosed herein can be readilyused as a source of energy avail- I able at temperatures above 10 C. toprovide the required heat source to enable the hydrogen-alloy complexesdisclosed in US. Patent No. 3,315,479 and US. Patent application S.N.642,289, to give 011 the hydrogen entrained therein. Thus small amountsof hydrogen can be contained in the instant alloys in a relatively smallpressure vessel which can provide a means to release large amounts ofhydrogen from large quantities of other hydrogen alloy complexes whichlatter complexes do not require pressure vessel containment at lowtemperatures. This advantage will greatly enhance the safety factorswhen such storage systems are employed in fuel cells and rockets as fueldepots. 1

In the preferred embodiment of our invention, the titanium-iron alloycontains 62 weight percent titanium and 38 weight percent iron based onthe total weight of the alloy. The alloys found usable in our inventioncan be produced by any convenient alloying technique. They can beproduced by simply heating the proper amounts of titanium and iron underan inert atmosphere with an induction heater until a melt is formed,intimately mixing the ingredients of the melt and thereafter cooling themelt until a solid alloy is formed. Liquid metal alloys are notdesirable for use in the practice of our invention because the pressurerequirements required to form the desired hydrogen-alloy complex wouldbe too great. Our invention is not limited to any particular physicalshape of the alloy, blocks and meshes of the alloy can be employed andindeed in certainapplications, such shapes may be desirable. In practicewhen hydrogen is adsorbed onto solid blocks of titanium-nickel alloysand desorbed therefrom, the solid block disintegrates into a pulverulentform. Conventional pressure vessels and heating. devices may be employedin the practice of our invention;

In the preferred embodiment of'our inventiomthe hy drogen and thetitanium-iron alloy are maintained at a temperature of 20 C. andmaintained under. a pressure of 200 pounds per square inch absoluteduring the loading operation. The pressure can be maintained byadiiingadditionali increments of hydrogen to the system tocounterbalance the increments taken up by the alloy during theabsorption phase of the process.

We haye found that about 4 atoms of hydrogen will be, adsorbed per atomof metal contained in. an alloy containing minimal amounts of iron. Onemol of. an. alloy having the composition corresponding to T igFe willabsorb up to 2 mols of hydrogen during the practice of our invention.

EXAMPLE I,

Apparatus.

An upright reactor vessel consisting of a stainlesssteel tube flanged.on the top end, and having; an inside diarneter of one inch, and a.length of about 4.0-inches; was titted. with anthermocouple well in thebottomendof thevessel. The bottom end of thevessel Wassealedandca-conneetion was fitted to the topof the=vesselto permit gasvto' be.with. drawn and introduced: in the vessel. The: vessel was in? sortedinto an electrically heated. furnace. Samples; were placed inthe vessel.

Procedure- A 6 gm. sample of an alloy consistingof. 68. by'weight.Tiand. 32 by weight Fe was weighed out in. a dry box- The sample waspulverized so. that it: could go through a .25 mesh screen (U .S.Standard sieve series-) be re. weigh dand introduced into thev vessel.The sample; was. immersed: in acetone so that it was not exposedito air.as:-

the vessel was. removed from the dry box. and introduced into theheater. Thevesselwas sealerl ,.evacuated. and the sample heated in vacuofor about. two hours at. a tern.- perature of 350 C. and allowed to coolto 20 C; H was admitted to. the vessel until a. pressure. of 400- p.s.i-.a. was r ac d App o ma e y 8 0 pe nt of he-Hiultima lr absorbedwas. absorbed in 32-4 minutes. When: absorption. was essentiallycomplete, thev reactor was at room tecrnr' p re nd ga eou w ve t from te y t m. til a predetermined. pressure of 1.4 p s.-.ila. was reached.The. a ple was h a ed o ab u 0 C- and low to com 7 4' to equilibrium andthe pressure recorded. At equilibrium, some gaseous l-l was removed fromthe system after which a new equilibrium was reached. When no further Hevolved from the sample upon removing gaseous H the entire cycle wasrepeated by re-adrnitting H into the system and re-absorbingH in thealloy.

Results.

tacting gaseous hydrogen with a solidtitanium-iron alloy,

said alloy being composed of'from about 35 weight percent to about 75weight percent titanium based on the total weight of the titanium-ironalloy and from about 25 weight percent to about weight percent ironbased upon the total weight of the titanium-iron alloy, whilemaintaining said hydrogen and-said allow at' a pressure ofi atv least14"pound's: per square inch an'dlat a temperature of' at. least. about1.0' C. until said alloy has: absorbed up to about: 3 weight percenthydrogen. based on the total weight: off the: titanium-iron. alloy.

2.. The method of: claim 1'. wherein said. alloy contains 68 weight:percent titanium and 32 weight percent ironbased. upon" the totaliweight. of the titaniumriron alloy.

3'. 'Iihe. method at. claim. 2. whereinsaid alloy and the hyd'mgenaaremaintained at a temperature of about 20 C.

and pressure: at 200. pounds per square inch.

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